Urinals in men's restrooms pose a health risk. While using a urinal the male's urine stream often creates splash-back spreading urine droplets on the user and his surroundings. Pasteur (1863) observed that human urine will readily support bacterial growth. The urine that has escaped the urinal can be tracked elsewhere, cause corrosion on features surrounding the urinal, creates a pungent odor in the bathroom, and often leads to embarrassment to the user when small wet spots created from the splash-back can clearly be seen on the user's clothing. The inventors of the current disclosure performed experiments to create a device that can be inserted into a urinal to prevent splash-back.
From experiments performed by the inventors of the current disclosure using an artificial male urethra and urine stream, it was observed that the liquid stream breaks into individual droplets due to the Plateau-Rayleigh instability as can be seen in FIG. 1. Previous laboratory work also showed that the splash caused by an impinging stream is nearly negligible, but that undesired splash-back is generated when droplet impact occurs. Thus the problem is simplified to a droplet impact incident. Splash-back occurs due to droplet impact onto a liquid film. Even if the surface is initially dry, the first impacting droplet effectively spreads to create a thin liquid film. When a droplet impacts a thin liquid film it forms a splash crown which rapidly expands outward from the point of impact as can be seen in FIG. 2. As this cylindrical sheet of fluid expands outward, a fluid instability on the top edge leads to the formation of satellite droplets 180 which are ejected during a splash event.